Flame-retardant poly lactic acid-containing  film or sheet, and method for manufacturing thereof

ABSTRACT

Provided is a film or sheet composed of a resin composition that includes a poly lactic acid (A), an acidic functional group-modified olefinic polymer (B) including an acidic functional group and having an acid value of 10 to 70 mg KOH/g and a weight average molecular weight of 10,000 to 80,000, a tetrafluoroethylene polymer (C), and an aromatic-condensed phosphoric acid ester-containing flame retardant (D) including a compound of General Formula (I) and in which the aromatic-condensed phosphoric acid ester-containing flame retardant (D) is included in an amount of 10 to 80 parts by weight based on 100 parts by weight of the poly lactic acid (A), and a method for manufacturing the film or sheet by melt film formation. Each sign in Formula is as described in the specification.

TECHNICAL FIELD

The present invention relates to flame-retardant poly lacticacid-containing films or sheets that have excellent flame retardancy,heat resistance, mechanical properties (for example, breaking strengthand tear strength), and roll lubricity.

BACKGROUND ART

A poly lactic acid resin is a biomass polymer and therefore has beendrawing attention in recent years in the context of the depletion ofpetroleum resources, the reduction of carbon dioxide emissions, and thelike.

However, poly lactic acid itself is readily burned and thus difficult tobe used for members that require flame retardancy, such as electricaland electronic applications. In addition, the poly lactic acid has a lowcrystallization rate and is unlikely to be crystallized by a common filmforming procedure. Thus, a film composed of a resin compositioncontaining the poly lactic acid has a problem of poor heat resistance.For example, such a film is thermally deformed at about 60° C. or morethat is a glass transition temperature of the poly lactic acid andcannot keep a film shape.

For providing desired flame retardancy and heat resistance to the polylactic acid resin, the following methods and the like have beendeveloped.

For example, there has been developed a method of providing the flameretardancy and heat resistance by the addition of aphosphorus-containing or nitrogen-containing flame retardant into amixture of a poly lactic acid resin and a heat resistant polymer such asa polycarbonate resin (Patent Documents 1 and 2). There has been alsodeveloped a method of providing the flame retardancy and heat resistanceby heat treating, at a particular temperature, a resin composition thatis obtained by the addition of a flame retardant to a mixture of a polylactic acid resin and an amorphous resin or a low-crystalline resin,during or after injection molding to highly crystallize the poly lacticacid resin (Patent Document 3).

However, either method does not provide sufficient effect on the problemwhen it is used for a film or sheet. In particular, there has beendeveloped no method that can be applied to a thin film having athickness of less than 200 μm until now.

Commonly, the smaller thickness a film or sheet has, the more difficultit is to satisfy a standard for flame retardancy (for example, UL-94 VTMstandards). To address this, a flame retardant is mixed in a largeramount. However, the flame retardant is a foreign matter to the polylactic acid resin, and thus such a poly lactic acid resin has a problemof the reduction of the breaking strength or tear strength.

There is another problem. That is, when a resin composition containingthe poly lactic acid is melted to form a film or sheet using metalrolls, the resin composition adheres to the metal rolls to interferewith the formation of the film or sheet because the resin compositionhas a poor releasability from the rolls.

For the heat resistance, there were reported methods for providing theheat resistance by accelerating the crystallization of the poly lacticacid resin by the following methods.

For example, there has been developed a method in which the poly lacticacid resin is subjected to, for example, melt extrusion to form a sheetand the sheet is biaxially stretched to accelerate stretching orientedcrystallization (Patent Document 4). However, this method has adisadvantage that a high operating temperature largely increases heatshrink due to internal stress during the stretching. Hence, the actualoperating temperature is at highest about 100° C.

A method of crystallization by the addition of a crystal nucleatingagent also has a problem. That is, in common film formation, a film iscooled to a glass transition temperature or less immediately after themelt film formation in order to keep the film shape, while the film hasa small thickness. Thus, the cooling rate is increased and theadvantageous effect of the crystal nucleating agent is unlikely to beachieved. To address the problem, it has been developed that a heatingstep at 60 to 100° C. is arranged for accelerating the crystallizationafter the film formation step (Patent Document 5). However, this methodis inefficient because a film is once cooled and solidified, and thenheated again.

CITATION LIST Patent Literature

-   Patent Document 1: Japanese Unexamined Patent Application No.    2006-182994-   Patent Document 2: Japanese Unexamined Patent Application No.    2008-303320-   Patent Document 3: Japanese Unexamined Patent Application No.    2007-308660-   Patent Document 4: Japanese Patent No. 330712-   Patent Document 5: Japanese Unexamined Patent Application No.    2007-130894

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a poly lacticacid-containing film or sheet having excellent flame retardancy, heatresistance, and roll lubricity while maintaining the original mechanicalproperties (for example, breaking strength and tear strength) of a polylactic acid resin and a method for manufacturing the film and sheet.

Solution to Problem

The present inventors have carried out intensive studies to solve theproblems, and as a result, the invention has been accomplished. Thepresent invention is as described below.

[1] A film or sheet (hereinafter, also referred to as a film or sheet ofthe present invention) composed of a resin composition (hereinafter,also referred to as a poly lactic acid (A)-containing resin composition)includes a poly lactic acid (A), an acidic functional group-modifiedolefinic polymer (B) that includes an acidic functional group and has anacid value of 10 to 70 mg KOH/g and a weight average molecular weight of10,000 to 80,000, a tetrafluoroethylene polymer (C), and anaromatic-condensed phosphoric acid ester-containing flame retardant (D)that includes a compound of General Formula (I). The aromatic-condensedphosphoric acid ester-containing flame retardant (D) is included in anamount of 10 to 80 parts by weight based on 100 parts by weight of thepoly lactic acid (A).

(where each A is independently an arylene group having 6 to 18 carbonatoms optionally further substituted with 1 to 3 alkyl groups having 1to 6 carbon atoms; each Y is independently a single bond or an alkylenegroup having 1 to 6 carbon atoms; each of X¹ to X⁴ is independently analkyl group having 1 to 14 carbon atoms, an aryl group having 6 to 18carbon atoms, an alkoxy group having 1 to 8 carbon atoms, or an aryloxygroup having 6 to 18 carbon atoms; k is an integer of 0 to 2; each of m1to m4 is independently an integer of 0 to 4; and n is an integer of 1 to5)

[2] In the film or sheet according to the aspect [1], the acidicfunctional group included in the acidic functional group-modifiedolefinic polymer (B) is a carboxylic acid anhydride group.

[3] In the film or sheet according to the aspect [1] or [2], thetetrafluoroethylene polymer (C) is included in an amount of 0.5 to 15.0parts by weight based on 100 parts by weight of the poly lactic acid(A).

[4] In the film or sheet according to any one of the aspects [1] to [3],the acidic functional group-modified olefinic polymer (B) is included inan amount of 0.1 to 10.0 parts by weight based on 100 parts by weight ofthe poly lactic acid (A).

[5] In the film or sheet according to any one of the aspects [1] to [4],the resin composition further includes a crystallization accelerator(E), and the crystallization accelerator (E) is included in an amount of0.1 to 5.0 parts by weight based on 100 parts by weight of the polylactic acid (A).

[6] The film or sheet according to any one of the aspects [1] to [5] hasa thickness of 10 to 500 μm, satisfies a flame-retardant standard ofUL94 VTM-0, and has a tear strength of 2.7 N/mm or more.

[7] The film or sheet according to any one of the aspects [1] to [6] hasa deformation rate of 40% or less under a load of 10 N for 30 minutes ina temperature environment of 150° C. in accordance with heat deformationtest in Japanese Industrial Standard C3005, and has a relativecrystallization rate of 50% or more calculated from Equation (1)

Relative crystallization rate (%)=(ΔHm−ΔHc)/ΔHm×100  (1)

(where ΔHc is an amount of heat of an exothermic peak associated withcrystallization of the film or sheet in a temperature rise process afterfilm formation, and ΔHm is an amount of heat associated with melting).

[8] A method for manufacturing the film or sheet according to any one ofthe aspects [1] to [7] includes forming a film from a resin compositionby melt film formation. In the method, the resin composition during themelt film formation has a temperature between a temperature 15° C.higher than a crystallization temperature (Tc) of the resin compositionin a temperature drop process and a temperature 5° C. lower than amelting temperature (Tm) in a temperature rise process, or the melt filmformed resin composition is cooled and solidified after acrystallization accelerating step between a temperature 25° C. lowerthan a crystallization temperature (Tc) of the resin composition in atemperature drop process and a temperature 10° C. higher than thecrystallization temperature (Tc).

[9] A method for manufacturing the film or sheet according to any one ofthe aspects [1] to [7] includes forming a film from a resin compositionby melt film formation. In the method, the resin composition during themelt film formation has a temperature between a temperature 15° C.higher than a crystallization temperature (Tc) of the resin compositionin a temperature drop process and a temperature 5° C. lower than amelting temperature (Tm) in a temperature rise process, and the meltfilm formed resin composition is cooled and solidified after acrystallization accelerating step between a temperature 25° C. lowerthan a crystallization temperature (Tc) of the resin composition in atemperature drop process and a temperature 10° C. higher than thecrystallization temperature (Tc).

In the method for manufacturing the film or sheet according to theaspect [8] or [9], the melt film formation is a technique of forming afilm having a desired thickness by passing the melted resin compositionthrough a space between two metal rolls.

[11] In the method for manufacturing the film or sheet according to anyone of the aspects [8] to [10], the crystallization accelerating step ischaracterized by bringing the melt film formed resin composition intocontact with a metal roll having a predetermined surface temperature.

Advantageous Effects of Invention

According to the present invention, a poly lactic acid-containing filmor sheet having excellent flame retardancy, heat resistance, and rolllubricity can be provided while maintaining the original mechanicalproperties (for example, breaking strength and tear strength) of polylactic acid.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a calender film formation machine.

FIG. 2 is a schematic view of a polishing film formation machine.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail.

The film or sheet of the present invention is composed of a resincomposition that includes a poly lactic acid (A), an acidic functionalgroup-modified olefinic polymer (B), a tetrafluoroethylene polymer (C),and an aromatic-condensed phosphoric acid ester-containing flameretardant (D). The film or sheet of the present invention includes atransparent film or sheet, a translucent film or sheet, and an opaquefilm or sheet.

The thickness of the film or sheet of the present invention is notnecessarily limited, but is commonly 10 to 500 μm, preferably 20 to 400μm, and more preferably, 30 to 300 μm.

[Poly lactic Acid (A)]

Lactic acid that is a material monomer of the poly lactic acid includesL- and D-optical isomers due to its asymmetric carbon atom. The polylactic acid (A) used in the present invention is a polymer mainlycomposed of L-lactic acid. A polymer containing a smaller amount ofD-lactic acid as an impurity during the manufacture has a highercrystallinity and a higher melting point. Hence, lactic acid to be usedpreferably has an L-lactic acid purity as high as possible, and thepurity of L-lactic acid is more preferably 95% or more. The poly lacticacid (A) used in the present invention may include other copolymerizablecomponents in addition to the lactic acid. Examples of other monomerunits include glycol compounds such as ethylene glycol, propyleneglycol, butanediol, heptanediol, hexanediol, octanediol, nonanediol,decanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, glycerin,pentaerythritol, bisphenol A, polyethylene glycol, polypropylene glycol,and polytetramethylene glycol; dicarboxylic acids such as oxalic acid,adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonicacid, glutaric acid, cyclohexanedicarboxylic acid, terephthalic acid,isophthalic acid, phthalic acid, naphthalenedicarboxylic acid,bis(p-carboxyphenyl)methane, anthracenedicarboxylic acid, 4,4′-diphenylether dicarboxylic acid, 5-sodium sulfoisophthalic acid, and5-tetrabutylphosphonium isophthalic acid; hydroxycarboxylic acids suchas glycolic acid, hydroxypropionic acid, hydroxybutyric acid,hydroxyvaleric acid, hydroxycaproic acid, and hydroxybenzoic acid; andlactones such as caprolactone, valerolactone, propiolactone,undecalactone, and 1,5-oxepan-2-one. The content of such an othercopolymerizable component is preferably 0 to 30% by mol and morepreferably 0 to 10% by mol based on the total monomer components.

The weight average molecular weight of the poly lactic acid (A) is, forexample, 10,000 to 400,000, preferably 50,000 to 300,000, and morepreferably 80,000 to 150,000. The melt flow rate of the poly lactic acid(A) at 190° C. under a load of 21.2 N [Japanese Industrial StandardK-7210 (test condition 4)] is, for example, 0.1 to 50 g/10 minutes,preferably 0.2 to 20 g/10 minutes, more preferably 0.5 to 10 g/10minutes, and particularly preferably 1 to 7 g/10 minutes. The polylactic acid (A) having a too high melt flow rate may form a film orsheet having poor mechanical characteristics and heat resistance. Thepoly lactic acid (A) having a too low melt flow rate may lead to a toohigh load during film formation.

In the specification, the “weight average molecular weight” means thatdetermined by gel permeation chromatography (GPC) (in terms ofpolystyrene). Conditions for GPC are as described below.

Column: TSKgel SuperHZM-H/HZ2000/HZ1000

Column size: 4.6 mm ID×150 mm

Eluant: chloroform

Flow rate: 0.3 ml/min

Detector: RI

Column temperature: 40° C.

Injection volume: 10 μl

The method for producing the poly lactic acid is not necessarily limitedand typical examples of the production method include lactide method anddirect polymerization method. The lactide method is as follows; lacticacid is heated and dehydrocondensed to give poly lactic acid having alow molecular weight; the poly lactic acid is heated and decomposedunder reduced pressure to give lactide that is a cyclic dimer of lacticacid; and the lactide is ring-opening polymerized in the presence of ametal salt catalyst such as tin(II) octanoate to give poly lactic acidhaving a high molecular weight. The direct polymerization method is asfollows; lactic acid is heated in a solvent such as diphenyl ether underreduced pressure to be polymerized while removing water in order tosuppress hydrolysis to give poly lactic acid directly.

A commercial product may be used as the poly lactic acid (A). Examplesof the commercial product include trade names “Lacea H-400” and “LaceaH-100” (manufactured by Mitsui Chemicals, Inc.) and trade names“TERRAMAC TP-4000” and “TERRAMAC TE-4000” (manufactured by UNITIKALTD.). A poly lactic acid (A) produced by a known or commonpolymerization method (for example, emulsion polymerization and solutionpolymerization) may be also used.

[Acidic Functional Group-Modified Olefinic Polymer (B)]

The manufacture of the film or sheet of the present invention requiresthe film formation by passing the melted poly lactic acid (A)-containingresin composition through a space between metal rolls with, for example,a calender film formation machine. Thus, the resin composition must bereadily removed from the metal roll surfaces. The acidic functionalgroup-modified olefinic polymer (B) included in the film or sheet of thepresent invention works as a lubricant to give a desired roll lubricityto the poly lactic acid (A)-containing resin composition.

Examples of the acidic functional group of the acidic functionalgroup-modified olefinic polymer (B) include a carboxyl group and groupsderived from it. The group derived form the carboxyl group is chemicallyderived from the carboxyl group, and examples include a carboxylic acidanhydride group, an ester group, an amide group, an imide group, and acyano group. The carboxylic acid anhydride group is preferred.

The acidic functional group-modified olefinic polymer (B) is obtainedby, for example, graft polymerization of an unmodified polyolefinpolymer with an unsaturated compound containing the “acidic functionalgroup” (hereinafter, also abbreviated to an acidic functionalgroup-containing unsaturated compound).

Examples of the unmodified polyolefin polymer include polymers includingpolyolefins such as high-density polyethylene, medium-densitypolyethylene, low-density polyethylene, polypropylene, polybutene,poly-4-methylpentene-1, a copolymer of ethylene and α-olefin, and acopolymer of propylene and α-olefin and oligomers of them; polyolefinelastomers such as ethylene-propylene rubber, ethylene-propylene-dienecopolymer rubber, butyl rubber, butadiene rubber, a low-crystallineethylene-propylene copolymer, a propylene-butene copolymer, anethylene-vinyl ester copolymer, an ethylene-methyl (meth)acrylatecopolymer, an ethylene-ethyl (meth)acrylate copolymer, anethylene-maleic anhydride copolymer, a blend of polypropylene andethylene-propylene rubber; and a mixture of two or more of them.Preferred are polypropylene, a copolymer of propylene and α-olefin,low-density polyethylene, and oligomers of them, and particularlypreferred are polypropylene, a copolymer of propylene and α-olefin, andoligomers of them. Examples of the “oligomers” include compoundsobtained from a corresponding polymer by thermal decomposition inaccordance with molecular weight reduction method. Such oligomers canalso be obtained by polymerization.

Examples of the acidic functional group-containing unsaturated compoundinclude a carboxyl group-containing unsaturated compound and anunsaturated compound containing a group derived from a carboxyl group.Examples of the carboxyl group-containing unsaturated compound includemaleic acid, itaconic acid, chloroitaconic acid, chloromaleic acid,citraconic acid, and (meth)acrylic acid. Examples of the unsaturatedcompound containing a group derived from a carboxyl group includecarboxylic acid anhydride group-containing unsaturated compounds such asmaleic anhydride, itaconic anhydride, chloroitaconic anhydride,chloromaleic anhydride, and citraconic anhydride; (meth)acrylic acidesters such as methyl (meth)acrylate, glycidyl (meth)acrylate, and2-hydroxyethyl (meth)acrylate; and (meth) acrylamide, maleimide, and(meth)acrylonitrile. Preferred are carboxyl group-containing unsaturatedcompounds and carboxylic acid anhydride group-containing unsaturatedcompounds, more preferred are carboxylic acid anhydride group-containingunsaturated compounds, and maleic anhydride is even more preferred.

Importantly, the acidic functional group-modified olefinic polymer (B)has a weight average molecular weight of 10,000 to 80,000, preferably15,000 to 70,000, and more preferably 20,000 to 60,000. The polymerhaving a weight average molecular weight of less than 10,000 may causebleed out after the formation of the film or sheet, and the polymerhaving a weight average molecular weight of more than 80,000 leads toseparation of the polymer from the poly lactic acid during rollkneading. Here, the bleed out means the phenomenon of bleeding of a lowmolecular weight component out to the surface of a film or sheet withtime after the film or sheet formation. In the specification, the“weight average molecular weight” means that determined by gelpermeation chromatography (GPC).

The acidic functional group in the acidic functional group-modifiedolefinic polymer (B) may be bonded to any position in the olefinicpolymer. The modified ratio is not necessarily limited, but the acidicfunctional group-modified olefinic polymer (B) commonly has an acidvalue of 10 to 70 mg KOH/g and preferably 20 to 60 mg KOH/g. The polymerhaving an acid value of less than 10 mg KOH/g cannot improve the rolllubricity, and the polymer having an acid value of more than 70 mg KOH/gcauses plate out to a roll. Here, the plate out to a roll means thatadhering or depositing of a component contained in the resincomposition, an oxidation, decomposition, combination, or degradationproduct of the component, or the like to a metal roll surface during themelt film formation of the resin composition using the metal roll. Inthe specification, the “acid value” means that determined byneutralization titration in accordance with Japanese Industrial StandardK0070-1992.

The acidic functional group-modified olefinic polymer (B) is obtained byreaction of the acidic functional group-containing unsaturated compoundand the unmodified polyolefin polymer in the presence of an organicperoxide. The organic peroxide to be used may be an initiator that iscommonly used for radical polymerization. Such reaction may be carriedout by either solution process or melting process.

In the solution process, a mixture of the unmodified polyolefin polymerand the acidic functional group-containing unsaturated compound isdissolved in an organic solvent together with an organic peroxide, andthe solution is heated to give the acidic functional group-modifiedolefinic polymer (B). The reaction temperature is preferably about 110to 170° C.

In the melting process, a mixture of the unmodified polyolefin polymerand the acidic functional group-containing unsaturated compound is mixedwith an organic peroxide, and the whole is melted and mixed for reactionto give the acidic functional group-modified olefinic polymer (B). Themelt-mixing can be carried out with various mixers such as an extruder,a Brabender, a kneader, and a Banbury mixer, and the kneadingtemperature is commonly from a melting point of the unmodifiedpolyolefin polymer to 300° C.

The acidic functional group-modified olefinic polymer (B) is preferablya maleic anhydride group-modified polypropylene. For the acidicfunctional group-modified olefinic polymer (B), commercial products maybe used, and examples include “Umex 1010” (maleic anhydridegroup-modified polypropylene, acid value: 52 mg KOH/g, weight averagemolecular weight: 32,000, modified ratio: 10% by weight), “Umex 1001”(maleic anhydride group-modified polypropylene, acid value: 26 mg KOH/g,weight average molecular weight: 49,000, modified ratio: 5% by weight),and “Umex 2000” (maleic anhydride group-modified polyethylene, acidvalue: 30 mg KOH/g, weight average molecular weight: 20,000, modifiedratio: 5% by weight), each manufactured by Sanyo Chemical Industries,Ltd.

The content of the acidic functional group-modified olefinic polymer (B)is not particularly limited and commonly 0.1 to 10.0 parts by weightbased on 100 parts by weight of the poly lactic acid (A). The content ispreferably 0.1 to 5.0 parts by weight and particularly preferably 0.3 to3.0 parts by weight in order to continue the roll lubricity effectwithout plate out to a roll and to maintain the biomass degree. Thepolymer having a content of less than 0.1 part by weight is unlikely toimprove the roll lubricity, and the polymer having a content of morethan 10.0 parts by weight cannot achieve effects corresponding to theamount added and reduces the biomass degree. Here, the biomass degreemeans the ratio of the dry weight of biomass used to the dry weight ofthe film or sheet.

[Tetrafluoroethylene Polymer (C)]

The tetrafluoroethylene polymer (C) included in the film or sheet of thepresent invention can improve the melt tension of the poly lactic acid(A)-containing resin composition and achieve oriented crystallization ina flow field in the melt film formation process to accelerate thecrystallization of the poly lactic acid (A). The tetrafluoroethylenepolymer (C) also works as a crystal nucleating agent for the poly lacticacid (A). Hence, the temperature setting of the resin compositionimmediately after the film formation to around a crystallizationtemperature can further accelerate the crystallization of the polylactic acid (A). Thus, the tetrafluoroethylene polymer (C) acceleratesthe crystallization of the poly lactic acid (A) and therefore canprovide heat resistance to the film or sheet of the present invention.The tetrafluoroethylene polymer (C) is also effective for the preventionof drip during the flame retardant evaluation described later of thefilm or sheet of the present invention.

The tetrafluoroethylene polymer (C) used in the present invention is ahomopolymer of tetrafluoroethylene or a copolymer of tetrafluoroethyleneand another monomer, and examples include polytetrafluoroethylene,perfluoroalkoxyalkane (a copolymer of tetrafluoroethylene andperfluoroalkyl vinyl ether), a perfluoroethylene propene copolymer (acopolymer of tetrafluoroethylene and hexafluoropropylene), anethylene-tetrafluoroethylene copolymer (a copolymer oftetrafluoroethylene and ethylene), and a copolymer oftetrafluoroethylene and perfluorodioxole. Polytetrafluoroethylene ispreferred.

It is supposed that the effect of the tetrafluoroethylene polymer (C) asa crystal nucleating agent on the poly lactic acid (A) depends on thecrystal structure of the tetrafluoroethylene polymer (C). Wide anglex-ray diffraction revealed that the poly lactic acid (A) had a crystallattice having an interplanar spacing of 4.8 angstroms while thetetrafluoroethylene polymer had a crystal lattice having an interplanarspacing of 4.9 angstroms. The results suggest that thetetrafluoroethylene polymer (C) can work as the crystal nucleating agentfor the poly lactic acid (A) due to an epitaxial effect. Here, theepitaxis means the crystal growth of the poly lactic acid (A) that isaligned with the crystal face on the crystal surface of thetetrafluoroethylene polymer (C) in the crystal growth of the poly lacticacid (A) on the surface of the tetrafluoroethylene polymer (C).

The tetrafluoroethylene polymer (C) has the same interplanar spacing asthat of a copolymer of tetrafluoroethylene and another monomer becausethe interplanar spacing depends on the crystal form of thetetrafluoroethylene moiety. Hence, as long as the crystal form of thepolytetrafluoroethylene is maintained and the physical properties arenot greatly changed, the amount of another monomer component in thecopolymer is not specifically limited, but is commonly preferably 5% byweight or less in the tetrafluoroethylene polymer (C).

The polymerization method of the tetrafluoroethylene polymer (C) is notparticularly limited but is specifically preferably emulsificationpolymerization. The tetrafluoroethylene polymer (C) obtained through theemulsification polymerization is readily fibrillated to readily form anetwork structure in the poly lactic acid (A). Then, this is supposed toimprove the melt tension of the resin composition including the polylactic acid (A) and to effectively accelerate the crystallization of thepoly lactic acid (A) in the flow field in the melt film formationprocess.

The weight average molecular weight of the tetrafluoroethylene polymer(C) is not particularly limited, and commonly 1,000,000 to 10,000,000and preferably 2,000,000 to 8,000,000.

Furthermore, for uniform dispersion in the poly lactic acid (A),particles of the “tetrafluoroethylene polymer (C)” may be modified witha polymer having high affinity to the poly lactic acid (A), such as a(meth)acrylic acid ester polymer. Examples of such a tetrafluoroethylenepolymer (C) include acrylic-modified polytetrafluoroethylene.

Commercially available tetrafluoroethylene polymers (C) may be used, andexamples of the commercially available polytetrafluoroethylene include“Fluon CD-014”, “Fluon CD-1”, and “Fluon CD-145” manufactured by ASAHIGLASS CO., LTD. Examples of the commercially available acrylic-modifiedpolytetrafluoroethylene include METABLEN (registered trademark), seriesA (for example, METABLEN A-3000 and METABLEN A-3800) manufactured byMITSUBISHI RAYON CO., LTD.

The content of the tetrafluoroethylene polymer (C) is commonly 0.5 to15.0 parts by weight based on 100 parts by weight of the poly lacticacid (A). The content is preferably 0.7 to 10.0 parts by weight andparticularly preferably 1.0 to 5.0 parts by weight in order to improvethe melt tension, to maintain the biomass degree, and to obtain a goodsurface condition. The polymer having a content of less than 0.5 part byweight is unlikely to improve the melt tension, and the polymer having acontent of more than 15.0 parts by weight cannot achieve effectscorresponding to the amount added and reduces the biomass degree.

[Aromatic-Condensed Phosphoric Acid Ester-Containing Flame Retardant(D)]

The aromatic-condensed phosphoric acid ester-containing flame retardant(D) included in the film or sheet of the present invention has an effectas a flame retardant to provide desired flame retardancy to the resincomposition including the poly lactic acid (A). The aromatic-condensedphosphoric acid ester-containing flame retardant (D) includes a compoundrepresented by General Formula (I).

(where each A is independently an arylene group having 6 to 18 carbonatoms optionally further substituted with 1 to 3 alkyl groups having 1to 6 carbon atoms; each Y is independently a single bond or an alkylenegroup having 1 to 6 carbon atoms; each of X¹ to X⁴ is independently analkyl group having 1 to 14 carbon atoms, an aryl group having 6 to 18carbon atoms, an alkoxy group having 1 to 8 carbon atoms, or an aryloxygroup having 6 to 18 carbon atoms; k is an integer of 0 to 2; each of m1to m4 is independently an integer of 0 to 4; and n is an integer of 1 to5)

Hereinafter, the definition of each group in General Formula (I) will bedescribed in details.

The “arylene group having 6 to 18 carbon atoms” in the “arylene grouphaving 6 to 18 carbon atoms optionally further substituted with 1 to 3alkyl groups having 1 to 6 carbon atoms” represented by A means adivalent aromatic hydrocarbon group having 6 to 18 carbon atoms.Examples of the group include phenylene groups (for example, a1,2-phenylene group, a 1,3-phenylene group, and a 1,4-phenylene group)and naphthylene groups (for example, a 1,2-naphthylene group, a1,3-naphthylene group, a 1,4-naphthylene group, a 1,5-naphthylene group,a 1,6-naphthylene group, a 1,7-naphthylene group, a 2,3-naphthylenegroup, a 2,4-naphthylene group, a 2,6-naphthylene group, and a2,7-naphthylene group). Preferred are phenylene groups (preferably a1,3-phenylene group and a 1,4-phenylene group) and naphthylene groups(preferably a 1,4-naphthylene group).

The “arylene group having 6 to 18 carbon atoms” may be furthersubstituted with 1 to 3 alkyl groups having 1 to 6 carbon atoms inaddition to two phosphate groups, and the alkyl groups may be the sameas or different from each other.

Here, the “alkyl group having 1 to 6 carbon atoms” means a straight orbranched saturated hydrocarbon group having 1 to 6 carbon atoms.Examples of the group include a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, an isobutyl group, a sec-butylgroup, a tert-butyl group, a pentyl group, an isopentyl group, aneopentyl group, a 1,2-dimethylpropyl group, a 1-ethylpropyl group, ahexyl group, an isohexyl group, a 1,2,2-trimethylpropyl group, a1,1-dimethylbutyl group, a 2,2-dimethylbutyl group, a 3,3-dimethylbutylgroup, and a 2-ethylbutyl group. Preferred are alkyl groups having 1 to4 carbon atoms, and more preferred are a methyl group and a tert-butylgroup.

A is preferably an arylene group having 6 to 18 carbon atoms [preferablya phenylene group (preferably a 1,3-phenylene group or a 1,4-phenylenegroup) or a naphthylene group (preferably a 1,4-naphthylene group)] thatmay be further substituted with 1 to 3 alkyl groups having 1 to 4 carbonatoms (preferably a methyl group or a tert-butyl group), and morepreferably a 1,3-phenylene group, a 1,4-phenylene group, a1,4-naphthylene group, or a 2-tert-butyl-5-methyl-1,4-phenylene group.

When two or more As are present, As may be the same as or different fromeach other and are preferably the same.

The “alkylene group having 1 to 6 carbon atoms” represented by Y means adivalent group derived from a straight or branched saturated hydrocarbonhaving 1 to 6 carbon atoms, and two bonds from the divalent group may beon the same carbon atom or different carbon atoms. Examples of the groupinclude a methylene group, an ethylene group, propylene groups (forexample, a 1,2-propylene group and a 1,3-propylene group), butylenegroups (for example, a 1,2-butylene group, a 1,3-butylene group, a1,4-butylene group, and a 2,3-butylene group), a 2-methyl-1,2-propylenegroup, a 2-methyl-1,3-butylene group, pentylene groups (for example, a1,2-pentylene group, a 1,3-pentylene group, a 1,4-pentylene group, a1,5-pentylene group, a 2,3-pentylene group, and a 2,4-pentylene group),hexylene groups (for example, a 1,2-hexylene group, a 1,3-hexylenegroup, a 1,4-hexylene group, a 1,5-hexylene group, a 1,6-hexylene group,a 2,3-hexylene group, a 2,4-hexylene group, a 2,5-hexylene group, and a3,4-hexylene group), a methylidene group, an ethylidene group, apropylidene group, an isopropylidene group, a butylidene group, anisobutylidene group, a sec-butylidene group, and a tert-butylidenegroup. Alkylene groups having 1 to 3 carbon atoms are preferred and amethyl group, an ethyl group, an ethylidene group, and an isopropylidenegroup are more preferred.

Y is preferably a single bond or an alkylene group having 1 to 3 carbonatoms and more preferably a single bond, a methyl group, an ethyl group,an ethylidene group, or an isopropylidene group.

When two or more Ys are present, Ys may be the same as or different fromeach other and are preferably the same.

The “alkyl group having 1 to 14 carbon atoms” represented by X¹, X², X³,or X⁴ means a straight or branched saturated hydrocarbon group having 1to 14 carbon atoms. Examples of the group include a methyl group, anethyl group, a propyl group, an isopropyl group, a butyl group, anisobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group,an isopentyl group, a neopentyl group, a 1,2-dimethylpropyl group, a1-ethylpropyl group, a hexyl group, an isohexyl group, a1,2,2-trimethylpropyl group, a 1,1-dimethylbutyl group, a2,2-dimethylbutyl group, a 3,3-dimethylbutyl group, a 2-ethylbutylgroup, a heptyl group, an isoheptyl group, an octyl group, an isooctylgroup, a nonyl group, an isononyl group, a decyl group, an isodecylgroup, an undecyl group, an isoundecyl group, a dodecyl group, anisododecyl group, a tridecyl group, an isotridecyl group, a tetradecylgroup, and an isotetradecyl group. Alkyl groups having 1 to 4 carbonatoms are preferred, and a methyl group and a tert-butyl group are morepreferred.

The “aryl group having 6 to 18 carbon atoms” represented by X¹, X², X³,or X⁴ means an aromatic hydrocarbon group having 6 to 18 carbon atoms.Examples of the group include a phenyl group and naphthyl groups (forexample, a 1-naphthyl group and a 2-naphthyl group).

The “alkoxy group having 1 to 8 carbon atoms” represented by X¹, X², X³,or X⁴ means a hydroxy group substituted with an alkyl group having 1 to8 carbon atoms among the above “alkyl groups having 1 to 14 carbonatoms”. Examples of the group include a methoxy group, an ethoxy group,a propoxy group, an isopropoxy group, a butoxy group, an isobutoxygroup, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, anisopentyloxy group, a neopentyloxy group, a 1,2-dimethylpropoxy group, a1-ethylpropoxy group, a hexyloxy group, an isohexyloxy group, a1,2,2-trimethylpropoxy group, a 1,1-dimethylbutoxy group, a2,2-dimethylbutoxy group, a 3,3-dimethylbutoxy group, a 2-ethylbutoxygroup, a heptyloxy group, an isoheptyloxy group, an octyloxy group, andan isooctyloxy group.

The “aryloxy group having 6 to 18 carbon atoms” represented by X¹, X²,X³, or X⁴ means a hydroxy group substituted with the above “aryl grouphaving 6 to 18 carbon atoms”. Examples of the group include a phenoxygroup and naphtyloxy groups (for example, a 1-naphtyloxy group and a2-naphtyloxy group).

Each of X¹, X², X³, and X⁴ is preferably alkyl groups having 1 to 14carbon atoms, more preferably alkyl groups having 1 to 4 carbon atoms,and even more preferably a methyl group and a tert-butyl group.

When two or more X is are present, X¹s may be the same as or differentfrom each other and are preferably the same. When two or more X²s arepresent, X²s may be the same as or different from each other and arepreferably the same. When two or more X³s are present, X³s may be thesame as or different from each other and are preferably the same. Whentwo or more X⁴s are present, X⁴s may be the same as or different fromeach other and are preferably the same.

Furthermore, X¹, X², X³, and X⁴ may be the same as or different fromeach other and are preferably the same.

k is an integer of 0 to 2.

Each of m1 to m4 is independently an integer of 0 to 4 and preferably aninteger of 0 to 2. m1, m2, m3, and m4 may be the same as or differentfrom each other and are preferably the same.

n is an integer of 1 to 5, preferably an integer of 1 to 3, and morepreferably 1.

The compound represented by General Formula (I) is preferably a compoundin which A is an arylene group having 6 to 18 carbon atoms [preferably aphenylene group (preferably a 1,3-phenylene group or a 1,4-phenylenegroup) or a naphthylene group (preferably 1,4-naphthylene group)] thatmay be further substituted with 1 to 3 alkyl groups having 1 to 4 carbonatoms (preferably a methyl group or a tert-butyl group) (preferably a1,3-phenylene group, a 1,4-phenylene group, a 1,4-naphthylene group, ora 2-tert-butyl-5-methyl-1,4-phenylene group); Y is a single bond or analkylene group having 1 to 3 carbon atoms (preferably a single bond, amethyl group, an ethyl group, an ethylidene group, or an isopropylidenegroup); X¹ to X⁴ are an alkyl group having 1 to 14 carbon atoms(preferably an alkyl group having 1 to 4 carbon atoms, and morepreferably a methyl group or a tert-butyl group); k is an integer of 0to 2; m1 to m4 are an integer of 0 to 2; and n is an integer of 1 to 3(preferably 1).

Examples of the compound represented by General Formula (I) include1,3-phenylene-bis(diphenyl phosphate), 1,3-phenylene-bis(di-2,6-xylenylphosphate), 1,4-naphthylene-bis(diphenyl phosphate),4,4′-biphenylene-bis(diphenyl phosphate),4,4′-p-terphenylene-bis(diphenyl phosphate), 4,4′-(methylenediphenyl)-bis(diphenyl phosphate), 4,4′-(ethylene diphenyl)-bis(diphenylphosphate), 4,4′-(ethylidene diphenyl)-bis(diphenyl phosphate),4,4′-(isopropylidene diphenyl)-bis(diphenyl phosphate) [another name,bisphenol A bis(diphenyl phosphate)], 4,4′-(isopropylidenediphenyl)-bis[di(2-t-butylphenyl)phosphate)], 4,4′-(isopropylidenediphenyl)-bis[di(2,4-di-t-butylphenyl)phosphate)], and4,4′-[isopropylidene-di(2-t-butyl-5-methylphenyl)]-bis(diphenyldiphosphate). Among them, preferred are 1,3-phenylene-bis(diphenylphosphate), 1,3-phenylene-bis(di-2,6-xylenyl phosphate), and4,4′-(isopropylidene diphenyl)-bis(diphenyl phosphate) from theviewpoint of compatibility with poly lactic acid and flame-retardanteffect. These compounds can be produced by a known method.

The aromatic-condensed phosphoric acid ester-containing flame retardant(D) includes at least one compound represented by General Formula (I) asa main component. Specifically, the content is commonly 90% by weight ormore and preferably 95% by weight to 100% by weight. Other components inthe aromatic-condensed phosphoric acid ester-containing flame retardant(D) is not specifically limited as long as the object of the presentinvention is not impaired.

For the aromatic-condensed phosphoric acid ester-containing flameretardant (D), commercial products may be used. Examples of thecommercial product include “PX-200”, “CR-741”, and “CR733S” manufacturedby DAIHACHI CHEMICAL INDUSTRY CO., LTD.

The aromatic-condensed phosphoric acid ester-containing flame retardant(D) is suitable for providing the flame retardancy to the poly lacticacid (A)-containing resin composition. It also has excellent hydrolysisresistance, and hence the flame retardancy is not reduced even when thefilm or sheet is used for a long time.

Furthermore, the aromatic-condensed phosphoric acid ester-containingflame retardant (D) is melted within a temperature range where the polylactic acid (A)-containing resin composition is melted and kneaded, andhas good compatibility with the poly lactic acid (A). Thus, theretardant is unlikely to reduce the original mechanical properties (forexample, breaking strength and tear strength) of the poly lactic acid(A) even when the retardant is contained in a large amount. Thearomatic-condensed phosphoric acid ester-containing flame retardant (D)has good compatibility with the poly lactic acid (A), and hence has aplasticization effect to improve brittleness of the poly lactic acid(A).

The content of the aromatic-condensed phosphoric acid ester-containingflame retardant (D) is commonly 10 to 80 parts by weight based on 100parts by weight of the poly lactic acid (A). The content is preferably15 to 60 parts by weight and more preferably 20 to 50 parts by weight inorder to preserve the flame retardancy in the UL94 VTM-0 standard and tosuppress the decrease of relative crystallization rate and the increaseof heat deformation rate. The retardant having a content of less than 10parts by weight cannot achieve the flame-retardant effect, and alsoprovides little plasticization effect. The retardant having a content ofmore than 80 parts by weight causes the reduction of mechanicalproperties (for example, breaking strength and tear strength) and bleedout.

The aromatic-condensed phosphoric acid ester-containing flame retardant(D) may inhibit the crystallization of the poly lactic acid (A) becausethe retardant has good compatibility with the poly lactic acid (A).However, the addition of the retardant in the amount described aboverequired for providing the flame retardancy little affects thecrystallization of the poly lactic acid (A) and does not inhibit theprovision of the heat resistance to the film or sheet of the presentinvention.

[Crystallization Accelerator (E)]

The resin composition of the present invention may include anothercrystallization accelerator (E) in addition to the tetrafluoroethylenepolymer (C). The crystallization accelerator (E) is not specificallylimited as long as it has a crystallization acceleration effect, but itis desirable to select a substance having a crystal structure that hasan interplanar spacing similar to the interplanar spacing of the crystallattice of the poly lactic acid (A). This is because a substanceincluding a crystal lattice having an interplanar spacing more similarto the interplanar spacing of the crystal lattice of the poly lacticacid (A) has a higher effect as a crystal nucleating agent for the polylactic acid (A). Examples of such a crystallization accelerator (E)include organic substances such as melamine polyphosphate, melaminecyanurate, zinc phenylphosphonate, calcium phenylphosphonate, andmagnesium phenylphosphonate and inorganic substances such as talc andclay. Among them, zinc phenylphosphonate is preferred because it has theinterplanar spacing most similar to the interplanar spacing of the polylactic acid (A) and can provide good crystallization accelerationeffect.

A commercially available crystallization accelerator (E) may be used.Examples of the commercially available zinc phenylphosphonate include“ECOPROMOTE” manufactured by Nissan Chemical Industries, Ltd.

The content of the crystallization accelerator (E) is commonly 0.1 to 5parts by weight based on 100 parts by weight of the poly lactic acid(A). The content is preferably 0.3 to 3 parts by weight in order tofurther accelerate the crystallization and to maintain the biomassdegree. The accelerator having a content of less than 0.1 part by weightis unlikely to accelerate the crystallization, and the acceleratorhaving a content of more than 5 parts by weight cannot achieve effectscorresponding to the amount added and reduces the biomass degree.

The poly lactic acid (A)-containing resin composition may includevarious additives as necessary as long as the object of the presentinvention is not impaired. Examples of such additives include knownantioxidants, ultraviolet absorbers, plasticizers, stabilizers, releaseagents, antistatic agents, colorants, and drip inhibitors.

For the flame retardant evaluation of the film or sheet of the presentinvention, a flammability test is carried out in accordance with UL94,VTM test (vertical flammability test for thin material) to classify thefilm or sheet into VTM-0, VTM-1, VTM-2, and NOTVTM. The criteria for theclassification are in accordance with “UL 94, the Standard for Safety ofFlammability of Plastic Materials for Parts in Devices and AppliancesTesting, the fifth edition” (Underwriters Laboratories Inc.).

It is preferable that the film or sheet of the present invention isclassified into VTM-0 in the test, that is, the film or sheet meetsVTM-0 in UL94 standard.

The tear strength of the film or sheet of the present invention isdetermined in accordance with “Paper-Determination of tearingresistance-Elmendorf tearing tester method” in Japanese IndustrialStandard P8116.

The film or sheet of the present invention preferably has a tearstrength of 2.7 N/mm or more.

More preferably, the film or sheet of the present invention has athickness of 10 to 500 μm, satisfies the flame-retardant standard ofUL94 VTM-0, and has a tear strength of 2.7 N/mm or more.

The film or sheet of the present invention satisfying theflame-retardant standard of UL94 VTM-0 and having a tear strength of 2.7N/mm or more can be achieved by limiting each content of the poly lacticacid (A), the acidic functional group-modified olefinic polymer (B), thetetrafluoroethylene polymer (C), and the aromatic-condensed phosphoricacid ester-containing flame retardant (D) within the range defined bythe present invention. In particular, it is important to limit thecontent of the aromatic-condensed phosphoric acid ester-containing flameretardant (D) within the range defined by the present invention.

The heat deformation rate of the film or sheet of the present inventionis determined in accordance with the heat deformation test in JapaneseIndustrial Standard C3005.

The film or sheet of the present invention preferably has a deformationrate of 40% or less under a load of 10 N for 30 minutes in a temperatureenvironment of 150° C.

The relative crystallization rate of the film or sheet of the presentinvention is calculated using Equation (1) from the amount of heat AHcof the exothermic peak associated with crystallization of a sample ofthe film or sheet in a temperature rise process after film formation andthe amount of heat AHm associated with the subsequent melting that aredetermined by DSC.

Relative crystallization rate (%)=(ΔHm−ΔHc)/ΔHm×100  (1)

The film or sheet of the present invention preferably has a relativecrystallization rate of 50% or more.

More preferably, the film or sheet of the present invention has adeformation rate of 40% or less under a load of 10 N for 30 minutes in atemperature environment of 150° C. in accordance with the heat test inJapanese Industrial Standard C3005 and has a relative crystallizationrate of 50% or more that is calculated from Equation (1).

In order to obtain the film or sheet of the present invention having adeformation rate of 40% or less and a relative crystallization rate of50% or more, it is important to limit each content of the poly lacticacid (A), the acidic functional group-modified olefinic polymer (B), thetetrafluoroethylene polymer (C), and the aromatic-condensed phosphoricacid ester-containing flame retardant (D) within the range defined bythe present invention, specifically, to limit the content of thetetrafluoroethylene polymer (C) and the content of thearomatic-condensed phosphoric acid ester-containing flame retardant (D)within the ranges defined by the present invention. In order to achievethe film or sheet of the present invention having a deformation rate of40% or less and a relative crystallization rate of 50% or more, it isalso important to employ, as the method for manufacturing the film orsheet of the present invention, a manufacturing method (described later)that includes forming a film from a poly lactic acid (A)-containingresin composition by melt film formation, in which the resin compositionduring the melt film formation has a temperature between a temperature15° C. higher than a crystallization temperature (Tc) of the resincomposition in a temperature drop process and a temperature 5° C. lowerthan a melting temperature (Tm) in a temperature rise process and/or themelt film formed resin composition is cooled and solidified after acrystallization accelerating step between a temperature 25° C. lowerthan a crystallization temperature (Tc) of the resin composition in atemperature drop process and a temperature 10° C. higher than thecrystallization temperature (Tc) [preferably between a temperature 10°C. higher than the crystallization temperature (Tc) and a temperature10° C. lower than the crystallization temperature (Tc)].

The film or sheet of the present invention may be used for applicationssimilar to those of common films or sheets, but in particular, can besuitably used as a base material of a pressure-sensitive adhesive filmor sheet.

The method for manufacturing the film or sheet of the present inventionis not particularly limited and is preferably a method of forming a filmfrom the poly lactic acid (A)-containing resin composition by melt filmformation. For example, the film or sheet of the present invention canbe manufactured by preparing the poly lactic acid (A)-containing resincomposition including each component that is homogeneously dispersed bya continuous melt kneader such as a twin screw extruder or a batch meltkneader such as a pressure kneader, a Banbury mixer, and a roll kneader,then by forming a film from the resin composition by an extrusion methodsuch as a T-die method and an inflation method, calendering, polishing,or the like, and by cooling and solidifying the film. The melt filmformation is preferably a technique of forming a film having a desiredthickness by passing the melted resin composition through a spacebetween two metal rolls, and is particularly preferably calendering andpolishing.

The thickness of the film or sheet of the present invention is properlyadjusted depending on the intended use, but is commonly 10 to 500 μm,preferably 20 to 400 μm, and particularly preferably 30 to 300 μm.

When the poly lactic acid (A)-containing resin composition is formedinto a film by the melt film formation, the temperature of the resincomposition during the melt film formation is not particularly limited,but is preferably between a temperature 15° C. higher than acrystallization temperature (Tc) of the resin composition in atemperature drop process and a temperature 5° C. lower than a meltingtemperature (Tm) in a temperature rise process. The adjustment to such atemperature accelerates the crystallization of the poly lactic acid (A)and readily provides the heat resistance to the film or sheet of thepresent invention.

For example, when the resin composition is melted to be formed into afilm by calendering, the temperature of the resin composition during thecalender rolling is adjusted to between a temperature 15° C. higher thana crystallization temperature (Tc) of the resin composition in atemperature drop process and a temperature 5° C. lower than a meltingtemperature (Tm) in a temperature rise process. Such rolling at amelting point or lower accelerates the oriented crystallization. Theacceleration effect on the oriented crystallization is much improved bythe combination of the tetrafluoroethylene polymer (C) with the resincomposition. The tetrafluoroethylene polymer (C) is fibrillated to forma network in the resin composition and also works as the crystalnucleating agent. It is supposed that such a synergistic effectaccelerates the oriented crystallization. Therefore, by the rollingwithin the temperature range, the film or sheet of the present inventioncan obtain a smooth surface condition as well as good heat resistancedue to the oriented crystallization acceleration effect (that is, thereduction of the relative crystallization rate is suppressed, and theincrease of the heat deformation rate is suppressed).

The method for manufacturing the poly lactic acid-containing film orsheet of the present invention may further include a step of controllinga temperature condition after the melt film formation in order toeffectively accelerate the crystallization by the tetrafluoroethylenepolymer (C). Specifically, the melt film formed resin composition may becooled and solidified after a step of accelerating the crystallization(hereinafter, also simply abbreviated to “crystallization acceleratingstep”) by once keeping the resin composition between a temperature 25°C. lower than a crystallization temperature (Tc) of the resincomposition in a temperature drop process and a temperature 10° C.higher than the crystallization temperature (Tc) [preferably between atemperature 10° C. higher than the crystallization temperature (Tc) anda temperature 10° C. lower than the crystallization temperature (Tc)].That is, the crystallization accelerating step is a step of subjectingthe melt film formed resin composition to a condition where thetemperature is controlled between a temperature 25° C. lower than acrystallization temperature (Tc) of the resin composition in atemperature drop process and a temperature 10° C. higher than thecrystallization temperature (Tc) [preferably between a temperature 10°C. higher than the crystallization temperature (Tc) and a temperature10° C. lower than the crystallization temperature (Tc)], and a step ofcapable of accelerating the crystallization of the resin compositionwhile maintaining the smooth surface condition after the melt filmformation. Examples of such a temperature control method include, butare not particularly limited to, a method of bringing the melt filmformed resin composition into direct contact with a roll, belt, or thelike that can be heated to a predetermined temperature.

In particular, the melt film formed resin composition is preferablybrought into contact with a metal roll having a predetermined surfacetemperature from the viewpoint of constant control at a predeterminedtemperature. Hence, also in the step, the poly lactic acid(A)-containing resin composition is desirably a composition that can bereadily removed from a metal roll, and from the viewpoint, the acidicfunctional group-modified olefinic polymer (B) is required to be added.

It is preferred that the time for the crystallization accelerating stepis as long as possible. The time is not necessarily limited because itfinally depends on the crystallization degree of the resin composition,but is commonly 2 to 10 seconds and preferably 3 to 8 seconds.

In the crystallization accelerating step, even when the crystallizationtemperature (Tc) of the resin composition in a temperature drop processis changed due to, for example, the addition of another crystalnucleating agent, the maximum temperature of an exothermic peakassociated with the crystallization in a temperature drop process ispreviously determined by DSC measurement to constantly give an optimumtemperature condition for the crystallization accelerating step. At thattime, the consideration to the shape change of the film or sheetobtained by heat at the temperature is little required, but the step ispreferably performed at a temperature at which the obtained film orsheet has a heat deformation rate of 40% or less.

The method for manufacturing the poly lactic acid-containing film orsheet of the present invention is preferably a method that includesforming a film from a poly lactic acid (A)-containing resin compositionby melt film formation. In the method, the resin composition during themelt film formation has a temperature between a temperature 15° C.higher than a crystallization temperature (Tc) of the resin compositionin a temperature drop process and a temperature 5° C. lower than amelting temperature (Tm) in a temperature rise process and/or the meltfilm formed resin composition is cooled and solidified after acrystallization accelerating step between a temperature 25° C. lowerthan a crystallization temperature (Tc) of the resin composition in atemperature drop process and a temperature 10° C. higher than thecrystallization temperature (Tc) [preferably between a temperature 10°C. higher than the crystallization temperature (Tc) and a temperature10° C. lower than the crystallization temperature (Tc)].

In the method for manufacturing the poly lactic acid-containing film orsheet of the present invention including the crystallizationaccelerating step, the resin composition is crystallized in thecrystallization accelerating step and then cooled and solidified. Hencethe internal stress is unlikely to remain, and the obtained film orsheet does not cause large heat shrink when it is used. Therefore, thehighly crystallized film or sheet of the present invention that isprepared by the manufacturing method can keep the shape to near themelting point of the poly lactic acid and can be sufficiently used forapplications that require heat resistance and that are not previouslyapplicable.

The manufacturing method has large advantages in economy andproductivity because it does not require inefficient steps of coolingand solidifying and then heating again.

It is desirable that the method for manufacturing the poly lacticacid-containing film or sheet of the present invention including thecrystallization accelerating step is continuously carried out from themelt film formation step, the crystallization accelerating step, to thecooling and solidifying step from the viewpoint of productivity becausesuch a system shortens the treatment time. Examples of such a methodinclude methods using a calender film formation machine, a polishingfilm formation machine, and the like.

FIG. 1 shows a schematic view of a calender film formation machine inone embodiment used in the manufacturing method. Hereinafter, FIG. 1will be described in detail.

Between four calender rolls, a first roll (1), a second roll (2), athird roll (3), and a fourth roll (4), the melted resin composition isrolled to gradually reduce the thickness. The rolling is adjusted sothat the resin composition will have a desired thickness after the resincomposition is finally passed through between the third roll (3) and thefourth roll (4). In the case of the calender film formation, the filmformation of the resin composition from the first to fourth rolls (1) to(4) corresponds to the “melt film formation step”. Take off rolls (5)having a temperature between a temperature 25° C. lower than acrystallization temperature (Tc) of the resin composition in atemperature drop process and a temperature 10° C. higher than thecrystallization temperature (Tc) [preferably between a temperature 10°C. higher than the crystallization temperature (Tc) and a temperature10° C. lower than the crystallization temperature (Tc)] are a roll groupwith which the melt film formed resin composition (8) is initially incontact. The roll group includes one or more rolls (three rolls inFIG. 1) and removes the melted resin composition (8) from the fourthroll (4). When a plurality of take off rolls (5) are used in this mannerand the temperature of each roll can be controlled, each roll preferablyhas the same temperature but may have a different temperature within adesired temperature range. A larger number of the take off rolls (5)increases the time for isothermal crystallization and has an advantagein the acceleration of crystallization. In the case of the calender filmformation, the crystallization of the melt film formed resin composition(8) is accelerated on the take off rolls (5), and thus the step ofpassing the resin composition (8) through the take off rolls (5)corresponds to the “crystallization accelerating step”.

Two cool rolls (6) and (7) cool and solidify the resin composition (8)by passing the resin composition (8) between them while forming thesurface into a desired shape. Thus, commonly, one roll (for example, thecool roll (6)) is a metal roll that has a surface designed for providinga surface shape to the resin composition (8), and the other roll (forexample, the cool roll (7)) is a rubber roll. In Fig. each arrow means arotation direction of a corresponding roll.

FIG. 2 shows a schematic view of a polishing film formation machine inone embodiment used in the manufacturing method. Hereinafter, FIG. 2will be described in detail.

An extruder leading end (10) of an extruder (not shown in the drawing)is placed between a heated second roll (2) and a heated third roll (3).Between the second roll (2) and the third roll (3), a melted resincomposition (8) is continuously extruded at a predetermined pushing-outspeed. The extruded resin composition (8) is rolled between the secondroll (2) and the third roll (3) to have a smaller thickness. The rollingis adjusted so that the resin composition will have a desired thicknessafter the resin composition is finally passed through between the thirdroll (3) and the fourth roll (4). In the case of the polishing filmformation, the film formation of the resin composition (8) from thesecond to fourth rolls (2) to (4) corresponds to the “melt filmformation step”. Then, the film is passed through three take off rolls(5) having a temperature between a temperature 25° C. lower than acrystallization temperature (Tc) of the resin composition (8) in atemperature drop process and a temperature 10° C. higher than thecrystallization temperature (Tc) [preferably between a temperature 10°C. higher than the crystallization temperature (Tc) and a temperature10° C. lower than the crystallization temperature (Tc)] and finallypassed through cool rolls (6) and (7) to prepare a solidified film orsheet. In the case of the polishing film formation, the step of passingthe resin composition through the take off rolls (5) corresponds to the“crystallization accelerating step”.

EXAMPLES

Hereinafter, the present invention will be further specificallydescribed with reference to examples and comparative examples. Thepresent invention is not intended to be limited to them. Evaluations inexamples and the like are carried out as follows.

Abbreviations of material names to be used in Table 1 are shown below.

[Poly lactic Acid (A)]

A1: Lacea H-400 (manufactured by Mitsui Chemicals, Inc.)

[Acidic Functional Group-Modified Olefinic Polymer (B)]

B1: maleic anhydride group-modified polypropylene (weight averagemolecular weight=49,000, acid value=26 mg KOH/g): Umex 1001(manufactured by Sanyo Chemical Industries, Ltd.)

B2: maleic anhydride group-modified polypropylene (weight averagemolecular weight=32,000, acid value=52 mg KOH/g): Umex 1010(manufactured by Sanyo Chemical Industries, Ltd.)

In order to be compared with the component (B1) and the component (B2),a component (B′) below was studied.

B′: unmodified low molecular weight polypropylene (weight averagemolecular weight=23,000, acid value=0 mg KOH/g): VISCOL 440P(manufactured by Sanyo Chemical Industries, Ltd.)

[Tetrafluoroethylene Polymer (C)]

C1: polytetrafluoroethylene: Fluon CD-014 (manufactured by ASAHI GLASSCO., LTD.)

C2: acrylic-modified polytetrafluoroethylene: METABLEN A-3000(manufactured by MITSUBISHI RAYON CO., LTD.)

[Aromatic-Condensed Phosphoric Acid Ester-Containing Flame Retardant(D)]

D1: 1,3-phenylene-bis(di-2,6-xylenyl phosphate): PX-200 (manufactured byDAIHACHI CHEMICAL INDUSTRY CO., LTD.), a powder having a melting pointof 95° C.

D2: bisphenol A bis(diphenyl phosphate): CR-741 (manufactured byDAIHACHI CHEMICAL INDUSTRY CO., LTD.), a liquid having a freezing pointof 4° C.

In order to be compared with the component (D1) and the component (D2),a component (D′) below was studied.

D′: melamine polyphosphate: MPP-A (manufactured by SANWA Chemical Co.,Ltd.), a powder having an average particle diameter of 4 μm

[Crystallization Accelerator (E)]

E1: zinc phenylphosphonate: ECOPROMOTE (manufactured by Nissan ChemicalIndustries, Ltd.)

Example 1

The raw materials above were mixed in a compounding ratio shown in Table1 to prepare a resin composition. The resin composition was melted andkneaded with a Banbury mixer, and then subjected to calender filmformation using a 4-roll inverted L calender so as to have a thicknessof 100 μm. Next, as shown in FIG. 1, three rolls (take off rolls) thatcould be heated at any temperature were placed immediately after themelt film formation step to arrange a crystallization accelerating stepwhere the melt film formed resin composition could be passed while theupper side and the lower side of the film alternately came in contactwith the rolls. Then, the resin composition was solidified by passingthrough cool rolls to prepare a film. The temperature of the resincomposition during the melt film formation was regarded as the surfacetemperature of the roll corresponding to the fourth roll (4) in FIG. 1,and for the temperature of the resin composition in the crystallizationaccelerating step, the surface temperatures of three take off rolls (5)in FIG. 1 were adjusted to substantially the same and regarded as thecrystallization acceleration temperature. The film formation speed was 5m/min, and the substantial time for the crystallization acceleratingstep (passage time through the take off rolls) was about 5 seconds.

Examples 2 to 10

Each resin composition was prepared in the compounding ratio shown inTable 1 and subjected to the same operation as that in Example 1 toprepare each film of Examples 2 to 10.

Comparative Examples 1 to 5

Each resin composition was prepared in the compounding ratio shown inTable 1 and subjected to the same operation as that in Example 1 toprepare each film of Comparative Examples 1 to 5.

<Melting Temperature>

The endothermic peak temperature associated with the melting of theresin composition in a temperature rerise process after film formationwas determined by DSC to be regarded as the melting temperature (Tm;also referred to as crystal melting peak temperature).

<Crystallization Temperature>

The exothermic peak temperature associated with the crystallization ofthe resin composition in a temperature drop process from 200° C. afterfilm formation was determined by DSC to be regarded as thecrystallization temperature (Tc; also referred to as crystallizationpeak temperature).

<Film Formability Result>

(1) Plate out to roll: A roll surface was visually observed andevaluated as “A” for no dirt on the roll surface, as “C” for any dirt onthe roll surface, and as “B” for any dirt on only a part of the rollsurface.(2) Releasability: The releasability was evaluated on the melt filmformed resin composition from the fourth roll (4) in FIG. 1. The resincomposition capable of being taken off onto the take off rolls (5) wasevaluated as “good”, and that incapable of being taken off onto the takeoff rolls (5) was evaluated as “poor”. Comparative Example 2 was notevaluated because it was not removed.(3) Film surface condition: It was visually observed. The film surfacethat was not rough but smooth was evaluated as “A”, that having bankmarks (irregularity due to uneven flow of the resin), shark skin, orpinholes was evaluated as “C”, and that having indistinctive bank marksor shark skin was evaluated as “B”. Comparative Example 2 was notevaluated because it was not removed.

<Relative Crystallization Rate>

The amount of heat ΔHc of the exothermic peak associated with thecrystallization of the film sample in the temperature rise process afterfilm formation and the amount of heat ΔHm associated with the subsequentmelting were determined by DSC to calculate the relative crystallizationrate using Equation (1). Comparative Example 2 was not evaluated becauseit was not removed.

Relative crystallization rate (%)=(ΔHm−ΔHc)/ΔHm×100  (1)

Acceptance evaluation: The film having a relative crystallization rateof 50% or more was regarded as acceptance.

The DSC used for determination of the crystallization temperature andthe relative crystallization rate and the measurement condition were asfollows.

Apparatus: DSC 6220 manufactured by SII NanoTechnology Inc.Conditions: measurement temperature region; from 20° C., 200° C., 0° C.,to 200° C.(That is, first, measurement was carried out in a temperature riseprocess form 20° C. to 200° C., then in a temperature drop process from200° C. to 0° C., and finally in a temperature rerise process from 0° C.to 200° C.)Temperature rise rate/temperature drop rate: 2° C./minMeasurement atmosphere: under a nitrogen atmosphere (200 ml/min)

No exothermic peak associated with the crystallization was observed inthe temperature rerise process. Hence, it was judged that 100% of acrystallizable region was crystallized at a temperature rise rate of 2°C./min, and the validity of the equation for the relativecrystallization rate was confirmed.

<Heat Deformation Rate>

The heat deformation rate was determined in accordance with the heatdeformation test in Japanese Industrial Standard C3005. The measurementapparatus and measurement conditions used are as follows.

Apparatus: Heat deformation tester manufactured by TESTER SANGYO CO.,LTD.Conditions: sample size: 1 mm thickness×25 mm width×40 mm length (filmswere stacked into a total thickness of 1 mm)Measurement temperature: 150° C.

Load: 10 N

Measurement time: 30 minutes (the test started without aging consideringrecrystallization)Calculation method of heat deformation rate: The thickness T1 before thetest and the thickness T2 after the test were determined, and the heatdeformation rate was calculated using Equation (2). Comparative Example2 was not evaluated because it was not removed.

Heat deformation rate (%)=(T1−T2)/T1×100  (2)

Acceptance evaluation: The film having a heat deformation rate of 40% orless was regarded as acceptance.

<Tear Strength>

The tear strength was determined in accordance with “Paper-Determinationof tearing resistance-Elmendorf tearing tester method” in JapaneseIndustrial Standard P8116. The measurement apparatus and measurementconditions used are as follows.

Apparatus: Elmendorf tear strength tester manufactured by TESTER SANGYOCO., LTD.Conditions: sample size: about 1 mm thickness×76 mm width×63 mm length(films were stacked into a total thickness of about 1 mm)

The sample was cut out so that the direction parallel to thelongitudinal direction would be the machine direction (hereinafterreferred to as MD direction) during the film formation.

Calculation method of tear strength: The tear strength was calculatedusing Equation (3). Comparative Example 2 was not evaluated because itwas not removed.

T=(A×p)/(n×t×1000)  (3)

T: tear strength (N/mm)

A: measured value (mN)

p: the number of test pieces to be the standard for pendulum scale (16in this apparatus)

n: the number of test pieces that are simultaneously torn

t: average thickness (mm) per test piece

Acceptance evaluation: The film having a tear strength of 2.7 N/mm ormore that was the tear strength of the film without a flame retardant inComparative Example 1 was regarded as acceptance.

<Flame-Retardant Test (UL-94 VTM)>

The flame-retardant test was carried out in accordance with UL94 VTMtest method (vertical flame test for thin materials). ComparativeExample 2 was not evaluated because it was not removed.

Acceptance evaluation: The film satisfying the VTM-0 standard wasregarded as acceptance.

<Acceptance Evaluation>

The film satisfying the acceptance standards of the tear strength andthe flame-retardant test (UL-94 VTM) was regarded as B, the filmsatisfying the acceptance standards of all evaluations was regarded asA, and the film not satisfying at least one of the acceptance standardsof the tear strength and the flame-retardant test (UL-94 VTM) wasregarded as C, for the acceptance evaluation.

Each evaluation result of Examples 1 to 10 and Comparative Examples 1 to5 is shown in Table 2 and Table 3.

TABLE 1 Material name A1 B1 B2 B′ C1 C2 D1 D2 D′ E1 Example 1 100 2.0 —— 3.0 — — 20 — — Example 2 100 — 3.0 — 6.0 — 60 — — 4.0 Example 3 100 —1.0 — — 5.0 30 — — — Example 4 100 4.0 — — — 9.0 — 50 — 1.0 Example 5100 — 0.5 — 1.0 — 15 — — 2.0 Example 6 100 — 1.0 — — 5.0 — 35 — —Example 7 100 3.0 — — — 12.0  — 40 — — Example 8 100 — 7.0 — — 2.0 30 —— — Example 9 100 1.0 — — 4.0 — — 30 — — Example 10 100 — 1.0 — 2.0 — 70— — — Comparative 100 — 2.0 — — 3.0 — — — — Example 1 Comparative 100 —— 3.0 — 2.0 20 — — 1.0 Example 2 Comparative 100 — 1.0 — — — — 25 — —Example 3 Comparative 100 — 3.0 — — 4.0 — — 30 — Example 4 Comparative100 — 2.0 — — 2.0  5 — — — Example 5 Unit: part by weight

TABLE 2 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam-Evaluation ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 8 ple 9 ple 10Film thickness (μm) 100 100 100 100 100 100 100 100 100 100 DSC data forresin Melting temperature 167 160 164 162 167 164 162 165 164 160composition (° C.) Crystallization 119 125 117 126 129 117 118 119 118117 temperature Setting temperature Resin temperature 150 150 150 155175 155 155 155 170 150 (° C.) during melt film formationCrystallization acceleration 120 125 115 125 130 100 115 120 150 115temperature Film formability Plate out to roll A A A A A A A B A Aresult Releasability Good Good Good Good Good Good Good Good Good GoodFilm surface condition A A A A A A B A A A Relative crystallization rate(%) 81 88 76 84 71 57 83 87 35 47 Heat deformation rate (%) 7 34 24 3719 39 10 7 55 71 Tear strength (N/mm) 3.3 3.6 3.0 3.5 3.2 3.1 2.9 2.83.5 3.8 UL-94 VTM VTM-0 VTM-0 VTM-0 VTM-0 VTM-0 VTM-0 VTM-0 VTM-0 VTM-0VTM-0 Acceptance evaluation A A A A A A B B B B

TABLE 3 Comparative Comparative Comparative Comparative ComparativeEvaluation Example 1 Example 2 Example 3 Example 4 Example 5 Filmthickness (μm) 100 — 100 100 100 DSC data for resin Melting temperature167 165 165 167 167 composition (° C.) Crystallization 120 129 116 120120 temperature Setting temperature Resin temperature 155 145 140 160155 (° C.) during melt film formation Crystallization acceleration 120130 115 120 120 temperature Film formability Plate out to roll A C A A Aresult Releasability Good Not removed Poor Good Good Film surfacecondition A — C A A Relative crystallization rate (%) 92 — 32 87 87 Heatdeformation rate (%) 2 — 61 3 7 Tear strength (N/mm) 2.7 — 2.4 1.6 2.8UL-94 VTM NG — VTM-0 VTM-0 VTM-2 Acceptance evaluation C C C C C

The evaluation results shown in Table 2 and Table 3 ascertained thateach film of Examples 1 to 10 of the present invention had excellentflame retardancy and a high tear strength. It was also ascertained thateach film of Examples 1 to 8 in which the roll setting temperature andthe amount of a flame retardant were optimized had a high relativecrystallization rate and a suppressed heat deformation rate. Each filmof Examples 1 to 6 in which the amount of the acidic functionalgroup-modified olefinic polymer and the amount of thetetrafluoroethylene polymer were also optimized had good releasabilityand a good film surface condition and did not cause the plate out to aroll.

In contrast, each film of Comparative Examples 1 to 5 that did notinclude the components or did not have the compounding ratio of thepresent invention did not satisfy all the desired flame retardancy andtear strength, and the total acceptance evaluation was C.

INDUSTRIAL APPLICABILITY

According to the present invention, a poly lactic acid-containing filmor sheet having excellent flame retardancy, heat resistance, and rolllubricity is provided while maintaining the original mechanicalproperties (for example, breaking strength and tear strength) of polylactic acid.

REFERENCE SIGNS LIST

-   -   1 First roll    -   2 Second roll    -   3 Third roll    -   4 Fourth roll    -   5 Take off roll    -   6 Cool roll    -   7 Cool roll    -   8 Resin composition    -   9 Bank (resin puddle)

1. A film or sheet composed of a resin composition comprising: a polylactic acid (A); an acidic functional group-modified olefinic polymer(B) including an acidic functional group and having an acid value of 10to 70 mg KOH/g and a weight average molecular weight of 10,000 to80,000; a tetrafluoroethylene polymer (C); and an aromatic-condensedphosphoric acid ester-containing flame retardant (D) including acompound of General Formula (I), the aromatic-condensed phosphoric acidester-containing flame retardant (D) being included in an amount of 10to 80 parts by weight based on 100 parts by weight of the poly lacticacid (A),

(where each A is independently an arylene group having 6 to 18 carbonatoms; each Y is independently a single bond or an alkylene group having1 to 6 carbon atoms; each of X¹ to X⁴ is independently an alkyl grouphaving 1 to 14 carbon atoms, an aryl group having 6 to 18 carbon atoms,an alkoxy group having 1 to 8 carbon atoms, or an aryloxy group having 6to 18 carbon atoms; k is an integer of 0 to 2; each of m1 to m4 isindependently an integer of 0 to 4; and n is an integer of 1 to 5). 2.The film or sheet according to claim 1, wherein the acidic functionalgroup included in the acidic functional group-modified olefinic polymer(B) is a carboxylic acid anhydride group.
 3. The film or sheet accordingto claim 1, wherein the tetrafluoroethylene polymer (C) is included inan amount of 0.5 to 15.0 parts by weight based on 100 parts by weight ofthe poly lactic acid (A).
 4. The film or sheet according to claim 1,wherein the acidic functional group-modified olefinic polymer (B) isincluded in an amount of 0.1 to 10.0 parts by weight based on 100 partsby weight of the poly lactic acid (A).
 5. The film or sheet according toclaim 1, wherein the resin composition further includes acrystallization accelerator (E), and the crystallization accelerator (E)is included in an amount of 0.1 to 5.0 parts by weight based on 100parts by weight of the poly lactic acid (A).
 6. The film or sheetaccording to claim 1 having a thickness of 10 to 500 μm, satisfying aflame-retardant standard of UL94 VTM-0, and having a tear strength of2.7 N/mm or more.
 7. The film or sheet according to claim 1 having adeformation rate of 40% or less under a load of 10 N for 30 minutes in atemperature environment of 150° C. in accordance with heat deformationtest in Japanese Industrial Standard C3005, and having a relativecrystallization rate of 50% or more calculated from Equation (1),Relative crystallization rate (%)=(ΔHm−ΔHc)/ΔHm×100  (1) (where ΔHc isan amount of heat of an exothermic peak associated with crystallizationof the film or sheet in a temperature rise process after film formation,and AHm is an amount of heat associated with melting).
 8. A method formanufacturing the film or sheet according to claim 1, the methodcomprising forming a film from a resin composition by melt filmformation, the resin composition during the melt film formation having atemperature between a temperature 15° C. higher than a crystallizationtemperature (Tc) of the resin composition in a temperature drop processand a temperature 5° C. lower than a melting temperature (Tm) in atemperature rise process or the melt film formed resin composition beingcooled and solidified after a crystallization accelerating step betweena temperature 25° C. lower than a crystallization temperature (Tc) ofthe resin composition in a temperature drop process and a temperature10° C. higher than the crystallization temperature (Tc).
 9. A method formanufacturing the film or sheet according to claim 1, the methodcomprising forming a film from a resin composition by melt filmformation, the resin composition during the melt film formation having atemperature between a temperature 15° C. higher than a crystallizationtemperature (Tc) of the resin composition in a temperature drop processand a temperature 5° C. lower than a melting temperature (Tm) in atemperature rise process and the melt film formed resin compositionbeing cooled and solidified after a crystallization accelerating stepbetween a temperature 25° C. lower than a crystallization temperature(Tc) of the resin composition in a temperature drop process and atemperature 10° C. higher than the crystallization temperature (Tc). 10.The method for manufacturing the film or sheet according to claim 8,wherein the melt film formation is a technique of forming a film havinga desired thickness by passing the melted resin composition through aspace between two metal rolls.
 11. The method for manufacturing the filmor sheet according to claim 8, wherein the crystallization acceleratingstep is characterized by bringing the melt film formed resin compositioninto contact with a metal roll having a predetermined surfacetemperature.